We propose to study the differentiation of mast cells and basophils using cell culture techniques. We will investigate whether mast cells and basophils come from the same or separate lineages. Our major approach is to establish clonal cell culture methods for both basophils and mast cells from the same species and to determine whether or not both types of cells are present in the same colony. Our laboratory has developed clonal cell culture methods for human basophils and mouse mast cells. We will attempt to develop clonal cultures of human mast cells from normal bone marrows and samples from systemic mastocytosis patients. Mast cells and basophils from guinea pigs will be studied because the ultrastructure of these cells has been well-characterized in this species. We will also study the growth requirements of mast cells and basophils. IL-3 has recently been shown to be very similar or identical to mast cell growth factor. We will study the mechanism of action of pure IL-3 on cloned murine mast cells. Preliminary information obtained in our laboratory indicates that conditioned media from the T-lymphocyte cell line, HUT 102, contains a growth factor for human pluripotent hemopoietic stem cells. We will attempt to identify a human homologue of IL-3 and determine whether it supports the growth of mast cells. Finally, we propose to analyze the mechanisms regulating mast cell proliferation using a computer simulation of a birth-death model. We will test the hypothesis that mast cells, like stem cells, proliferate in a stochastic fashion and if so, we will characterize the factors affecting the parameters of the model.